1. Field of the Invention
The present invention relates to a tension-free continuous thermal treatment of fibers, and more particularly to a method of and an apparatus for carrying out such thermal treatment of fibers.
2. Prior Art
In the manufacture of synthetic fibers, it is a general practice that fibers having been spun from a polymer are drawn and then subjected to a thermal treatment to become stable against deformation when they are subjected to various subsequent treatments. In general, the fibers shrink while being heat treated. As a usual thermal treatment, the bundle of fibers is made to pass through continuously touching the surface of heated roll or heated stationary surface. In the above continuous method, it is impossible to keep the fibers in a state free from tension. Accordingly even the fibers while have been already heat-treated in the above way, tend to shrink to same extent when warmed upto the same temperature as that of the previous treatment. For the purpose of heat treating the fibers while being kept completely free from tension, there is another method in which the fibers are kept in an autoclave free from any stress during the heat treatment. This method is batch process and cannot be operated continuously.
The U.S. Pat. No. 3,763,527 issued on Oct. 9, 1973 which is assigned to the present assignee, discloses one such tension-free continuous thermal treatment. According to the disclosed treatment, the bundle of fibers withdrawn from a stuffer box in crimped or corrugated form is wrapped with a breathable heat resistant textile fabric and then passes through a heat-treatment chamber into which saturated steam of a temperature above 100.degree. C. is supplied under pressure to heat set the crimped fibers. The fibers are not bound lengthwise while being heat-treated, so that the fibers can shrink freely. The heat-treatment chamber has an inlet duct serving as a pressure seal within which saturated steam flows in a direction opposite to the direction of the movement of the fiber to expel air from spaces between the fiber to the outside of the heat-treatment chamber. So the steam distributes to all of the interspace among the fibers, the saturated steam occupying the inter-fiber spaces gives its latent heat to the fibers and condenses. The condensation of the preceding steam enables penetration of the succeeding steam and facilitates a continuous heat exchange between the saturated steam and the fibers with the result that the fibers are effectively treated in a relatively short period of time under tension-free conditions.
The above continuous method has proven to have unsatisfactory points. Namely: In the case where the treating temperature is high, the pressure of the saturated steam is also high, accordingly the mechanism of the inlet and outlet ducts must be complicated. Furthermore for keeping good sealing in the inlet and outlet ducts, the special type of crimper is required to keep the uniform shape of the cake withdrawn from a stuffer box. Usually fibers to be treated include water, of which steam is also required and condenses for heating up. Accordingly the heating medium turns to be mixture of steam and water. The quantity of the included water is not always uniform along the bundle of fibers, and the distribution of the component of the heating medium is not always uniform. This non-uniformity sometimes tends to cause non-uniformity of the effect of heat-treatment.